Submarine-cable telegraphy



June 1 1926. 1,586,961

0. E. BUCKLEY SUBMARINE CABLE TELEGRAPH]! Filed May 31 1922 PatentedJune 1,

unirsn STATES fil 'f lCE,

OLIVER E. BUCKLEY, OF MAPLEWOOD, NEW JERSEY, ASSIG'NOB TO WESTERN ELEC-TRIC COMPANY, INCORPORATED, 0]? NEW YORK, N. Y., ,A CORYORATION OF NEWYORK.

SUBMARINE-GABLE TELEGRAPHY.

Application filed May 31, 1922. Serial No. 564,793.

This invention relates to electrical transmission and particularly tosubmarine telegraphy. An object of the invention is to provide a novelmethod and means for signaling over transmission line simultaneously inbothdirections. A further object is to provide a method and means foropen ating a long loaded telegraph cable simultaneously in bothdirections at high signal speeds. I

Submarine telegraph cables of the ordinary non-loaded type are commonlyoperated simultaneously in two directions to a great advantage, theoutgoing and the incoming signals at each end being separated by meansof a duplex bridge comprising two approximately equal ratio arms and anartilicial line closely simulating the cable as regards its electricalcharacteristics. Dilfi culty is encountered, however, when an attempt ismade to apply this method of oporation to long loaded telegraph cables.This difficulty arises from the variability of the inductance andresistance of theloaded cable which makes it difficult to secure anartificial line that will giveas good a balance with a loaded cable asis commonly obtained in practice with non-loaded cable.

A. method which has sometimes been employed on short loaded telegraphcables where the degree of balance obtainable does not permitsimultaneous two-way operation with currents of a given frequency, is toemploy one range of frequency for sig naling in one direction andanother range of frequency for signaling in the opposite direction, theoutgoing and incoming signals at each end of, the cable being separatedby the combined use of a balancing network and a filter. In this caseneitherthe duplex bridge with its arti ficial line nor the filter wouldbe sufficient by itself to prevent interference between outgoing andincoming signals. However, by the combination of the two, simultaneoustwo-way operation is successfully secured.

It is well known that, the traffic capacity of long telegraph cables,when operated in one direction only is limited by the extraneousdisturbances to which the cable is subject." These disturbances may becaused by electrical ap aratus or machinery in the neighborhooc of thecable terminals, and in this case, of course, can be reduced orremoved-but are mere often of natural. origin and similar in characterto the well-known static of wireless telegraphy in which case they areunavoidable except by special construction of the cable. In commonoperat ing practice with non-loaded cables the transmitting voltage islimited by considerations of safety, and the highest speed obtainablefor one-way operation is that at which the signal, transmitted at themaxi mum permissible voltage, is received with sufficient intensity. tobe legible on the sensitive recording apparatus which, of course,records both the interference and thesignal. The requirement oflegibility demands that the received signal be of substantially greateramplitude than the extraneous interference lying in the same frequencyband as the sig nal. Otherwise, the interfering disturbances will maskthe signal and cause errors in reading the transmitted messages.Interfen ence of higher frequency than the frequency band of the signalcan, of course, be eliminated by means of suitable filters, so it isonly interference of the frequencies lying within the frequency band ofthe signal which is of serious consequence. The same considerationsapply to one-way operation of a long loaded. cable if operated byautomatic or recording means, except that by virtue of the inductiveloading the limiting speed set by interference is much higher than forthe non-loaded cable.

In the method of operation accordingto this invention it is proposed tooperate the loaded cable in one direction by means of automatic orrecording means and at a speed such that the received signal is ofgreater amplitude than the interference, and to operate itsimultaneously inthe other direction by a modulated wave train offrequency higher than any involved in the signal sent in the firstdirection. Thus a low frequency channel is provided in one direction anda relatively high frequency channel in the other direction. Since thelow frequency channel is operated up to the limit set by interference,and since the high frequency signals are attenuated more than the low'frequency signals, it follows that the amplitude of the high frequencysignals will not be large, and may even be small, in comparison withthat of the interference. Hence, if automatic or recording meanswcre'used to re ceive the high frequency si nal, the received wouldrendered by the in.

terference. In order to make it possible to read the high frequencysignal through the interference, it is proposed to make use of receptionby ear. To accomplish this the received signal will be amplified to sucha strength that it is audible in a telephone receiver. Now it is a factthat afskilled individual can by this means read signals which would bequite undecipherable if recorded by such means as an oscillograph. Theindividual is able to concentrate his attention on the tone of thesignal, and although the interfering disturbance may be many times theamplitude of the signal, he will, if sufficiently skilled in the art, beable to read messages without error through the interference.Experiments have shown that with interference of the characterencountered in submarine cables, an operator can distinguish and read atelegraphic signal by car through interference of average amplitude morethan ten times the amplitude of the signal and having peak values morethan a hundred times the amplitude of the signal. It has further beenfound by experiment that an operator can read audible signals consistingofwave trains in which the highest frequency involved is only of theorder of cyclesper second.

In order to make the invention more clear an installation will bedescribed and some definite figures of frequencies and speeds given. Theaccompanying drawing shows schematically a preferred embodiment of theinvention.

A submarine cable 1, which may be of the continuously loaded typeterminates in duplex bridges containing the usual blocking condensers 2,2, and artificial lines 3, 3 to balance the cable at the respectiveends. The artificial line 3 should be balanced with particular care forthe high frequency signals, and the artificial line 8, for the lowfrequency signals. At one terminal is an automatic transmitter i, whichmay conveniently be of the type commonly employed in submarine cabletelcgraphy, or of the type employed in multiplex printing telegraphy.Transmitter 62 sends messages composed of impulses of variable length,spacing and polarity through the cable to the receiving apparatus at thedistant end. At the other terminal of the cable is transmittingarrangement 6 comprising a key which serves to transmit wave trainsgenerated by an alternator, the key serving to regulate the length ofthe wave trains in the manner commonly employed for alternating currenttelegraphy. Signals transmitted by the key of the transmitter 6 arereceived through the transformer 7, a high pass filter 8, amplifier 9and telephone receivers 10. The function of the high pass filter, whichis an electrical networr which permits frequencies above a certain valueto be" transmitted and represses frequencies belowthat value, is toassist in eliminating from the high frequency signal, which it isdesired to receive, the low frequency disturbance which would beotherwise caused by the simultaneous low fre quency transmission in thereverse direction. The function of the amplifier, which may beconveniently of the well-known audion type, is to increase the intensityof the signals sufficiently to make them conveniently audible. Thesignals from the transmitter l are received through a network at thedistant end consisting of a low pass filter 14, a combined amplifier andshaping network 12 and a recording receiving device 13. The function ofthe low pass filter 1a is to eliminate from the low frequencysignahwhichitis desired to receive, disturbances created by the transmission of thehigh frequency signal. The function of the amplifier and shaping networkis to increase the amplitudeof the low frequency signal so that it maybe successfully recorded and to restore the shape of the signal so thatit may be legible in the recording apparatus. The structures of highpass and low pass filters, amplifiers and shaping networks are wellknown and they are hence shown only diagrammatically. The nature of thereceived signals is indicated by the curves shown above the respectiveterminal apparatus.

For the sake of giving definite figures let the cable be of thecontinuously loaded type in which a layer of permalloy, an alloy ofnickel and iron of high permeability, is used to secure high inductance.Let us assume a cable of 2300 miles in length loaded with permalloy tapehaving such dimensions and permeability as to give an inductance of 60milhenries per nautical mile. On

such a cable it is anticipated that the average amplitude of unavoidableinterference at the signaling frequency will be approximately onemicroampere. lVith a transmitting voltage of 50 volts the low frequencysignals may then be transmitted at such a speed that the received signalhas an amplitude of, let us say, 5 microamperes in order not to be madeillegible by the interference. This will permit a speed correspondingroughly to 60 cycles, and the low frequency signal will thus consume thefrequency band from O to 60 cycles. Signals may be sent in the reversedirection by a wave train of fundamental frequency of 130 cycles and ata voltage of 50, this being the limit set my considerations of safety,giving a received current at this frequency of .2 microampere, whichwill be of smaller amplitude than the interference, but which willnevertheless be legible through it by i I a car. Let us suppose that thesignaling speed in the high frequency channel corresponds to 20 cyclesper second, then the frequency bandoccu'pied by the high frequencysignal will be from 13020 or 110 cycles to 130+20 or 150 cycles, leavingthe frequency band from cycles tollO cycles to provide for the frequencyoverlap of the filters. It is to be understood that the above figuresare only given as illustrative, and the particular values of frequencyand current amplitude will have to be chosen by trial for eachinstallation.

Although I have described my invention with reference to two-wayoperation, it is pointed out that both the high frequency and lowfrequency channel may be operated in. one direction and the sameprinciples of reception may be taken advantage of. For someinstallations it is expected that more than one high frequency channelmay be used, separation between channels being made by appropriatefilters. It may be desirable to equip the terminal from which directcurrent signals are ordinarily sent with an auxiliary set of apparatuslike that at the other terminal, and to equip the termi nal from whichalternating current is ordinarily sent with an auxiliary set ofapparatus like that at the direct current transmitting terminal, so thatdirect current signals may be transmitted in the direction in whichtraffic is greatest at any given time.

What is claimed is:

1. The method of signaling over a submarine telegraph cable whichcomprises simultaneously transmitting two trains of signals, one trainof signals being trans mitted as a series of impulses of variable lengthand spacing and received with amplitude substantially greater thanordinary extraneous disturbances, and the other bein transmitted as amodulated sine wave an received with amplitudes substantially less thansuch extraneous disturbances.

2. The method of signaling over a submarine telegraph cable whichcomprises simultaneously transmitting trains of signals in oppositedirections, the transmission frequencies being different for each train,one train of signals being transmitted as a series of impulses ofvariable length and spacing received with amplitudes substantiallygreater than the extraneous disturbances, and the other beingtransmitted as a modulated wave train and received with amplitudessubstantially less than that of the op positely directed signals.

8. The method of operating a loaded submarine telegraph cable whichconsists in transmitting signals in one direction at a speed such as togive received signals large in comparison with ordinary extraneousdisturbances, and transmitting signals of substantially lower receivedcurrent strength in the opposite direction.

4. The method of signaling over a sub marine cable of such characterthat signals are highly attenuated which comprises simultaneouslytransmitting two trains only of signals, the transmission consisting oftransmitting in one direction with direct current signals only and inthe other direction with alternating current signals only, the lattersignals being transmitted as a modulated sine wave.

5. The combination with a submarine cable of such character that duplexbalanced circuits cannot be relied upon to separate outgoing fromincoming signals involving the same frequency range, ofterminalapparatus including such duplex balance circuits, means fortransmitting direct current signals in one direction only, and means fortransmitting alternating current signals in the opposite direction only.

6. The combination with a long telegraph cable, of balanced-bridgeterminal circuits including artificial balancing lines, means fortransmitting signal currents in one direction, means for transmittingsignal currents involving a different frequency range in the oppositedirection, transmission being limited to said two one-way channels, andterminal frequency filters for aiding in the separation of outgoing fromincoming signals.

7. The combination with a long heavilyloaded submarine cable, of meansfor transmitting direct current signals from one terminal, means fortransmitting modulated carrier current. signals from one terminal in therange of from 75 to 300 cycles per second, transmitting voltages beinglimited to the range of forty to seventy five volts, and automatic meansfor receiving and recording said direct current signals, said cablehaving such characteristics as to attenuate the modulated currentsignals to the order of ordinary extraneous disturbances or less and thedirect current signals to an amplitude not less than several times thatof said disturbances.

In witness whereof, I hereunto subscribe my name this 26th day of May A.D., 1922.

OLIVER E. BUCKLEY.

submarine

